Concerned about weight on the second floor of my house

I live in a house that I'm told was built in the 1920s. Wood frame from what I can tell. My father keeps a storage room on the second floor. It's the smallest room in the house...no smaller than 10' x 10' and no bigger than 12' x 12'. My concern is that the room is absolutely stuffed with bookcases full of books and boxes full of books. Full boxes are stacked to the ceiling. There are a few metal filing cabinets too (all filled). The room is so stuffed that the door just barely has enough room to swing open. There could easily be 1000+ lbs of books alone (not to mention the bookcases, boxes, and filing cabinets) and more are being added all the time.

Is this safe? What kind of weight would you guess a 70-80 year old wood frame home could take on the second floor? The room is right above the living room, so if it ever did collapse, both people and pets could be killed.

I've included a rough sketch (not to scale) to give you an idea of layout and weight distribution (as much as I can remember...it's been years since I've seen past the door). The key things to keep in mind are that everything is pretty much stacked to the ceiling and it has been this way for 5-10 years.

I'm trying to figure out whether I should be unconcerned about this or if I need to get the basement cleaned out ASAP (everything will eventually be moved to the basement, but I've been lazy about getting stuff cleaned out).

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Concerned about weight on the second floor of my house

We would need to know the size of the floor joists (2x6 to 2x12) and their current condition (splits, insect damage, warping, etc.). Since it's unlikely you have blueprints for a 90 year old structure, I can only think of pulling a 2nd floor board to look at the joists. As far as condition, do you see any wall cracks or spots where the floor is not level?

Concerned about weight on the second floor of my house

and it has been this way for 5-10 years.
The room is right above the living room,

Ayuh,... If it ain't fallin' in Yet,.. it's probably Ok...

Do you see any sags in the ceiling of the living room,..??

Your drawing is fine, but I'd be more concerned about the wall lay-outs in the floor below, 'n the support under those walls in the cellar...
The load of the room is transfered to the walls of the room, which are carried by Whatever is below That...
Think about it from the cellar floor, Up to that room...

Your drawing shows 2 of the walls are exterior,.. No problem there, they carry down to the foundation...
What I see as the point of concern would be what's Under the area by the door into the room, 'n the interior walls...

Concerned about weight on the second floor of my house

The density of paper is approximately 45 pounds per cubic foot. You do not indicate the height of the stacked paper, however you said it was up to the ceiling. Let us assume that there is 6 feet of books, paper etc. on the floor. That would produce a net floor load of close to 300 pounds per square foot, which coincidentally is about what libraries are designed for.

There is NO WAY that house was ever designed for 300 psf. Modern load criteria for living space calls for a live load of 40 psf (IBC 2009). The load you describe could easily be 7 times the standard design live load for a modern house. Older houses often were designed for 30 psf, in some cases 20 psf.

Exactly how strong the house was built is a totally different issue, since we have no way of knowing at this point whether the house was built to any standard at all. We do know that the floor has apparently not yet collapsed, likely a testament to the conservative nature of design codes, the intrinsic strength of wood, and some good fortune.

If this were a house I were living in, I would certainly plan to get the majority of the books out of that room. I would never assume that just because it has been OK for x years it will remain OK, wood has a nasty habit of creeping and eventually failing when it is overloaded.